Availability evaluation device and availability evaluation method

ABSTRACT

Workload is mitigated when customizing adding a state transition resulting from a datacenter operation procedure, to an availability evaluation model of a server infrastructure, provided as a standard library. This involves: storing in a state transition storage unit (STSU) definitions of a plurality of state transitions corresponding to system configurations; storing in an additional STSU definitions of state transitions used in system operation, which are different from the plurality of state transitions; receiving definitions of state transitions and registering the definitions in the additional STSU; analyzing system availability based on the definitions of the state transitions stored in the STSU and the definitions of the state transitions stored in the additional STSU; analyzing common state transition patterns in at least part of definitions of the plurality of state transitions used when operating the system, and stored in the additional STSU; and outputting analysis results on the common state transition patterns.

BACKGROUND

The present invention relates to an availability evaluation device andan availability evaluation method.

In recent years, a datacenter service that provides online serverinfrastructures (virtual machines or physical servers) to a number oftenant companies has become widespread. In providing such a service, itis important to evaluate the availability of systems so that the servicelevel requested from each tenant is fulfilled. In evaluation of thesystem availability, a datacenter administrator customizes anavailability evaluation model provided in advance for providing serverinfrastructures by taking a datacenter operation procedure such assetting changes or rebooting according to service level requirements oruse characteristics of tenants into consideration. Moreover, theavailability is calculated and verified based on the customizedavailability evaluation model.

Examples of techniques relating to a system that manages an availabilityevaluation model used when evaluating the availability are disclosed inPatent Documents 1 to 4. For example, Patent Document 1 discloses amethod of predicting an operating ratio of an entire system based oninformation on system characteristics such as a failure rate in anindividual computer of the system or a failure repair time andmonitoring information on failures in operation. Moreover, PatentDocument 2 discloses a method of forming a fault tree for making faultdetermination based on system configuration information related tosoftware and hardware and analyzing whether a fault rate calculatedbased on the fault tree meets a reference value. Further, PatentDocument 3 discloses a method of registering information on functions,configurations, securities, performances, and the like includingavailability as metadata at the time of installing an applicationprogram or an application service and using the metadata in the analysisof configuration management, failure detection, diagnosis, repair, andthe like. Furthermore, Patent Document 4 discloses a method of storing afault duration period and the number of users who were not able to useservices due to faults whenever faults occur, storing these items ofdata, and estimating a fault duration ratio, a fault suffering ratio peruser, an operating rate, and the like.

In particular, as for hardware, a method of analyzing the probability offaults in an entire system from the characteristics of components of asystem using a mathematical model such as a fault tree is widely known.On the other hand, as for software, a method of describing statetransitions using a mathematical model such as stochastic petri networkand reproducing the transitions through simulations to analyzeavailability is generally known. The availability is an index thatindicates the ratio in which users can use a service in a certain periodand is used as a synonym of an operating ratio. For example, if there isa period in which on average a user cannot use a service for one minutea day, the availability is 1−1/(24×60)=99.93%. In general, theavailability is determined from a failure occurrence interval (mean timebetween failure) and a failure repair period (mean time to repair).

An example of calculating or verifying the availability from anavailability evaluation model using the technique of such a stochasticpetri network will be described below. FIG. 13 shows a stochastic petrinetwork that defines state transitions of a virtual machine (alsoreferred to as VM).

In a stochastic petri network, each state is represented by a rectanglewith rounded corners. Here, a state “in operation” that indicates astate where a machine operates normally and a state “user VM stopped”that indicates a state where a user cannot use a service due to afailure are defined. A user VM is a general virtual machine that isallocated to a user and the user can access rather than a hypervisorthat indicates a control program of a virtual machine that only adatacenter administrator can access.

Moreover, each transition is represented by a rectangle that indicatesan event that causes a transition and an arrow that indicates thedirection of the transition. Here, it is defined that a transition from“in operation” to “user VM stopped” occurs due to an even “occurrence offailure” and a transistor from “user VM stopped” to “in operation”occurs due to an even “repair of failure.”

Although such a representation that is easily recognized visually asshown in FIG. 13 is easy for humans to understand, it is convenient tomanage state transitions in a form of a table shown in FIG. 14 whenstochastic Petri net analysis is implemented by a computer. This tableis called a state transition management table. In the state transitionmanagement table, an event name, a transition source state name, atransition destination state name, and a transition probability aredescribed for each event. For example, if a failure occurs with aprobability of 0.015, and a virtual machine is in the “in operation”state, the state transitions to the “user VM stopped” state.

Based on such a state transition management table, it is possible toreproduce transitions through simulations and to analyze availability.In this case, a state table shown in FIG. 15 is used. In the statetable, a state name and the number of tokens are described. Insimulations, in order to analyze how many virtual machines are in thedefined states, the number of virtual machines in the respective statesis substituted with a concept of the number of tokens. For example, ifthere are 10 virtual machines in total, and all virtual machines are inoperation, ten tokens are located in the “in operation” state, and zero(0) token is located in the “user VM stopped” state. Moreover, when astate transition occurs in any one virtual machine, one token moves.That is, the total number of tokens is constant. For example, it isassumed that when a simulation was started to cause state transitions tooccur according to a transition probability, two failures occurred. Inthis case, as shown in FIG. 15, a state where eight tokens are locatedin the “in operation” state, and two tokens are moved to the “user VMstopped” state is created.

Moreover, the value of availability can be calculated from the ratewhere at least one tokens are located in the “user VM stopped” state.The value of availability changes depending on the definition offailures and operations. For example, if it is regarded that a systemoperates normally when at least a half of virtual machines areoperating, the state of FIG. 15 where two tokens are located in the“user VM stopped” state can be regarded as a state where the systemoperates normally.

Patent Document 1: Patent Publication JP-T-2008-532170

Patent Document 2: Patent Publication JP-A-2006-127464

Patent Document 3: Patent Publication JP-T-2007-509404

Patent Document 4: Patent Publication JP-A-2005-080104

However, an availability evaluation model represented by stochasticpetri networks is one that is customized by a datacenter administratorbased on an availability evaluation model for a server infrastructure,which is standardly provided in a library of a system, by taking theserver infrastructure characteristics and the datacenter operationprocedure associated with the server infrastructure into consideration.That is, it is necessary to create various availability evaluationmodels according to the operation procedure. Thus, when dealing with anew tenant company and defining a new operation procedure, thedatacenter administrator needs to customize the availability evaluationmodels by taking the server infrastructure characteristics and thedatacenter operation procedure associated with the server infrastructureinto consideration.

Such a customization operation involves extracting all state transitionsof the server infrastructures, which can occur resulting from adatacenter operation procedure, without exception and designing indetail how these state transitions will be incorporated into anavailability evaluation model such as a stochastic petri network thatdescribes individual server infrastructures such as virtual machines.Thus, the datacenter administrator has to repeatedly perform such acomplicated customization operation whenever a tenant company or anoperation procedure is added, and the workload increases.

SUMMARY

The invention has been made in view of the above problems, and an objectof the present invention is to mitigate a workload when performingcustomization for adding a state transition resulting from a datacenteroperation procedure to an availability evaluation model of serverinfrastructures, which is standardly provided as a library.

An availability evaluation device according to a first aspect of thepresent invention includes: a state transition storage unit that storesdefinitions of a plurality of state transitions corresponding toconfigurations of a system; an additional state transition storage unitthat stores definitions of state transitions that are used whenoperating the system and that are different from the plurality of statetransitions; an operation registration unit that receives thedefinitions of the state transitions used when operating the system andregisters the definitions in the additional state transition storageunit; an availability analyzing unit that analyzes the availability ofthe system based on the definitions of the state transitions stored inthe state transition storage unit and the definitions of the statetransitions stored in the additional state transition storage unit; anoperation analysis unit that analyzes common state transition patternsin at least part of definitions of the plurality of state transitionsused when operating the system, and stored in the additional statetransition storage unit; and an operation analysis result output unitthat outputs analysis results obtained by the operation analysis unit.

In the present invention, a “unit” does not mean a physical means onlybut includes a case where the function of the “unit” is realized bysoftware. Moreover, the function of one “unit” or device may be realizedby two or more physical means or devices, and the functions of two ormore “units” or devices may be realized by one physical means or device.

According to the present invention, it is possible to mitigate aworkload when performing customization for adding a state transitionresulting from a datacenter operation procedure to an availabilityevaluation model of server infrastructures, which is standardly providedas a library.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration example of an availabilityaccording to an embodiment of the present invention.

FIG. 2 shows an example of an availability evaluation model showing aplurality of state transitions corresponding to configurations of asystem of a virtual machine server.

FIG. 3 is a view showing an example of an operation registration table.

FIG. 4 is a view showing an example of a state transition added to anavailability evaluation model.

FIG. 5 is a view showing an example of a state transition added to anavailability evaluation model.

FIG. 6 is a view showing an example of a state transition added to anavailability evaluation model.

FIG. 7 is a view showing an example of an additional state transitionregistration table corresponding to an additional operation.

FIG. 8 is a flowchart showing an example of the operation of anavailability evaluation device.

FIG. 9 is a view showing an example of an availability evaluation modelin which cases where an operation procedure succeeds and fails are takeninto consideration.

FIG. 10 is a view showing an example of an availability evaluation modelin which cases where an operation procedure succeeds and fails are takeninto consideration.

FIG. 11 is a view showing an example of an availability evaluation modelin which cases where an operation procedure succeeds and fails are takeninto consideration.

FIG. 12 is a view showing an example of an additional state transitionregistration table.

FIG. 13 is a view showing an example of a stochastic petri network thatdefines state transitions of a virtual machine.

FIG. 14 shows an example of a state transition management table.

FIG. 15 is a view showing an example of a state table.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 1 is a view showing a configuration example of an availabilityevaluation device according to an embodiment of the present invention.An availability evaluation device 10 is a device that evaluatesavailability of a virtual machine server 20 that provides a virtualmachine to a user. The availability evaluation device 10 is aninformation processing device such as an application server and isconfigured to include a processor, a memory, an input device, a storagedevice, and the like.

Moreover, as shown in FIG. 1, the availability evaluation device 10 isconfigured to include a library management unit 30, a state transitionmanagement table (state transition storage unit) 32, an operationregistration unit 34, an operation registration table 36, an additionalstate transition registration table (additional state transition storageunit) 38, an availability analyzing unit 40, an availability analysisresult presentation unit 42, an operation analysis unit 4, and anoperation analysis result presentation unit 46. The library managementunit 30, the operation registration unit 34, the availability analyzingunit 40, the availability analysis result presentation unit 42, theoperation analysis unit 4, and the operation analysis resultpresentation unit 46 can be realized when processor executes a programstored in a memory, for example. Moreover, the state transitionmanagement table 32, the operation registration table 36, and theadditional state transition registration table can be realized using astorage area of a memory or a storage device.

The library management unit 30 manages the state transition managementtable 32 corresponding to an availability evaluation model (stochasticpetri network) of a virtual machine. Management means being provided amechanism for maintaining these management tables permanently and beingable to register, update, and refer to the management tables.

FIG. 2 shows an example of an availability evaluation model showing aplurality of state transitions corresponding to configurations of asystem of the virtual machine server 20. The availability evaluationmodel is managed in the library management unit 30 as the statetransition management table 32 as shown in FIG. 14, for example. In thestate transition management table 32, an event name, a transition sourcestate name, a transition destination state name, and a transitionprobability are included. The system configuration of the virtualmachine 20 includes basic software such as a network device such asserver hardware (physical server), a router, a switch, or a loadbalancer, and a user OS, in addition to virtual machines. The librarymanagement unit 30 can manage the state transition management table 32representing the availability evaluation model corresponding to thesesystem components as well as virtual machines.

Returning to FIG. 1, the operation registration unit 34 provides afunction of managing customization of state transitions occurring due toan operation procedure of the virtual machine 20 and manages theoperation registration table 36 and the additional state transitionregistration table 38.

FIG. 3 shows an example of the operation registration table 36. As shownin FIG. 3, the operation registration table 36 includes an operationname, an operation procedure, and an event name for each operation. Theoperation may be the granularity of an entire bunch of operations andmay be the granularity of part of operations. As shown in FIG. 3, theoperation registration table 36 may directly describe the specificcontent (workflow) of an operation procedure and may describe the nameor the like of a document or a command script that describes theoperation procedure so that the document or the command script can bereferred to.

The state transition corresponding to such an operation procedure isunique to the operation procedure and is not described in theavailability evaluation model corresponding to the system configurationof the virtual machine 20 that is included in the state transitionmanagement table 32 managed by the library management unit 30. Thus, inorder to evaluate the availability with the operation procedure alsotaken into consideration in addition to the system configuration, it isnecessary to customize the availability evaluation model according to anaddition of operation procedure.

FIGS. 4 to 6 show examples of state transitions added to theavailability evaluation model shown in FIG. 2. For example, in FIG. 4,an operation in which an “in operation” state transitions to a “user VMstopped” state is added according to a “restart of VM” event. Moreover,in FIG. 5, an operation in which a “guest OS stopped” state transitionsto the “in operation” state is added according to a “start of guest OS”event. Further, in FIG. 6, an operation in which the “guest OS stopped”state transitions to the “in operation” state is added according to a“network setting” event. FIG. 7 shows an example of the additional statetransition registration table 38 corresponding to these additionaloperations. As shown in FIG. 7, the format of the additional statetransition registration table 38 is similar to the format of the statetransition management table 32 and includes the event name, thetransition source state name, the transition destination state name, andthe transition probability of the availability evaluation model for eachevent.

The names of operations, events, states, and the like in the statetransition management table 32, the operation registration table 36, andthe additional state transition registration table 38 may be optionalcharacter strings and symbols as long as they do not overlap and can beused as identifiers.

Returning to FIG. 1, the availability analyzing unit 40 performssimulations on the availability evaluation model using the state tableshown in FIG. 15 based on the state transition management table 32managed by the library management unit 30 and the additional statetransition registration table 38 managed by the operation registrationunit 34 to calculate the availability of the system.

The availability analysis result presentation unit 42 provides aninterface for presenting the availability calculated by the availabilityanalyzing unit 40 to the datacenter administrator. The analysis resultmay be presented, for example, by displaying on a screen, printing outusing a printer, outputting a predetermined format of data, and thelike.

The operation analysis unit 44 interprets the additional statetransition registration table 38 managed by the operation registrationunit 34 to analyze the characteristics of the definitions of statetransitions corresponding to operations. For example, the operationanalysis unit 44 extracts customization patterns (pairs of transitionsource states and transition destination states) that occur frequentlyamong the definitions of the state transitions registered in theadditional state transition registration table 38. In the case of theadditional state transition registration table 38 shown in FIG. 7, theset of “in operation” and “user VM stopped” states occurs once, and theset of “guest OS stopped” and “in operation” states occurs twice. Sincethe number of occurrences of the latter is larger than the former, theoperation analysis unit 44 selects the pattern (the set of “guest OSstopped” and “in operation” states) as the most frequent customizationpattern. The operation analysis unit 44 can extract the most frequentcustomization pattern by aggregating the number of occurrences of allsets of states which can occur from the defined states.

The operation analysis result presentation unit 46 presents the analysisresult of the operation analysis unit 44. For example, the operationanalysis result presentation unit 46 provides an interface forpresenting the customization patterns extracted by the operationanalysis unit 44 to the datacenter administrator. The analysis resultmay be presented, for example, by displaying on a screen, printing outusing a printer, outputting a predetermined format of data, and thelike. For example, the operation analysis result presentation unit 46can present the analysis result to the datacenter administrator bydisplaying the frequent customization patterns extracted by theoperation analysis unit 44 on a screen. In addition to the set of “guestOS stopped” and “in operation” states, the operation analysis resultpresentation unit 46 may further display the “start of guest OS” and“network setting” which are the event names of the stochastic petrinetwork corresponding to this set.

The analysis result presented to the datacenter administrator in thismanner can be used as reference information for the datacenteradministrator when adding new operations to the additional statetransition registration table 38. For example, the extractedcustomization patterns may be displayed on a registration screen of theadditional state transition registration table 38, and the extractedcustomization patterns may be configured to be selectable in the inputfields of transition source and transition destination state names.Thus, it is possible to mitigate the load of the customization operationperformed by the datacenter administrator whenever tenant companies areadded and operation procedures are added.

An example of the operation of the availability evaluation device 10will be described with reference to the flowchart of FIG. 8. First, whendealing with a new tenant company and defining a new operationprocedure, the operation registration unit 34 receives definitions ofstate transitions of the added operation from the datacenteradministrator and registers the definitions in the operationregistration table 36 (S801). As a result, an operation name, anoperation procedure, and an event name of the corresponding stochasticpetri network are registered in the operation registration table 36.Further, the operation registration unit 34 receives the event name ofthe stochastic petri network, the transition source state name, thetransition destination state name, and the transition probabilitycorresponding to the newly created operation from the datacenteradministrator and registers the same in the additional state transitionregistration table 38 (S802).

Subsequently, the availability analyzing unit 40 calculates the systemavailability including the operation procedure of the virtual machineserver 20 by referring to the state transition management table 32managed by the library management unit 30 and the additional statetransition registration table 38 newly registered by the operationregistration unit 34 (S803). The availability analysis resultpresentation unit 42 presents the analysis result on the availability tothe datacenter administrator by displaying the value of the availabilitycalculated by the availability analyzing unit 40 on a screen, forexample, (S804).

The operation analysis unit 44 determines by counting whether the numberof operations in the operation registration table 36 registered by theoperation registration unit 34 has reached 100 (S805). The operationanalysis unit 44 may determine the number of newly registered operationsby referring to the additional state transition registration table 38rather than the operation registration table 36. If the number of newlyregistered operations is smaller than 100 (S805: NO), the flow returnsto the start and the process (S801 and S802) of registering in theoperation registration table 36 and the additional state transitionregistration table 38 and the availability evaluation process (S803 andS804) are repeated.

If the number of added operations has reached 100 (S805: YES), theoperation analysis unit 44 finds the most frequently occurring statetransition pattern within the additional state transition registrationtable 38 and selects the state transition pattern as the most frequentcustomization pattern (S806). Moreover, the operation analysis resultpresentation unit 46 presents the analysis result on the characteristicsof state transitions occurring when operating the system to thedatacenter administrator by displaying the selected frequentcustomization pattern on a screen, for example, (S807).

The number 100 is an example, and for example, another number may be setas a threshold value based on the operation policy of the datacenter.Moreover, rather than using the number of operations, the operationanalysis unit 44 may perform the analysis every predetermined period(for example, every 30 days). Further, rather than simply using the mostfrequent state transition pattern, a most frequent state transition onpattern under such a condition that a transition source is a specificstate, a most frequent state transition pattern under such a conditionthat a transition probability has a specific value or more, and the likemay be selected as the frequent customization pattern.

The present embodiment has been described above. According to theavailability evaluation device 10 of the present embodiment, theanalysis result on the state transitions registered in the additionalstate transition registration table 38 is presented to the datacenteradministrator. Thus, it is possible to mitigate the workload ofcustomization for adding state transitions resulting from the operationprocedure of the virtual machine 20 to the availability evaluation modelof the virtual machine server 20 which is standardly provided as alibrary.

The present embodiment is for a better understanding of the presentinvention and is not for limiting interpretation of the presentinvention. Various changes and improvements can be made withoutdeparting from the spirit and scope of the present invention, and theirequivalents are also included within the scope of the present invention.

For example, as shown in FIGS. 9 to 11, the present invention can alsodeal with a case of customizing an availability evaluation model bytaking cases where an operation procedure succeeds and fails intoconsideration. For example, the example shown in FIG. 9 shows that it islikely that the “in operation” state transitions (does not change) tothe “in operation” state if “restart of VM” succeeds, and that the “inoperation” state transitions to the “user VM stopped” state if “restartof VM” fails. Moreover, FIG. 10 shows a customized availabilityevaluation model in which state transitions resulting from the caseswhere the datacenter operation procedure for “start of guest OS”succeeds and fails are added. Further, FIG. 11 shows a customizedavailability evaluation model in which state transitions resulting fromthe cases where the datacenter operation procedure for “network setting”succeeds and fails are added.

In this case, the operation registration unit 34 receives event names ofthese stochastic petri network, transition source state names,transition destination state names for the success case, transitiondestination state names for the failure case, and success probabilitiesfrom the datacenter administrator and registers the same in theadditional state transition registration table 38. FIG. 12 shows anexample of the additional state transition registration table 38 forthat case. The additional state transition registration table 38 hassuch a format that the transition destination state name for the successcase, the transition destination state name for the failure case, andthe success probability are registered unlike the additional statetransition registration table 38 shown in FIG. 7.

In the example of FIG. 12, the set of “in operation,” “in operation,”and “user VM stopped” states occurs once, and the set of “guest OSstopped,” “in operation,” and “network stopped” states occurs twice. Thenumber of occurrences of the latter set is the larger among the twopatterns. Thus, the operation analysis unit 44 can select the set of“guest OS stopped,” “in operation,” and “network stopped” states as amost frequent customization pattern.

This application claims the benefit of priority based on Japanese PatentApplication No. 2010-263498, filed Nov. 26, 2010, the entire contents ofwhich are incorporated herein by reference.

Although the present invention has been described with reference to theembodiment, the present invention is not limited to the aboveembodiment. Various modifications that can be conceived by those skilledin the art can be made to the configuration and details of the presentinvention within the scope of the present invention.

Part or all of the embodiments are described in the following additionalnotes but are not limited thereto.

(Additional Note 1)

An availability evaluation device comprising: a state transition storageunit that stores definitions of a plurality of state transitionscorresponding to configurations of a system; an additional statetransition storage unit that stores definitions of state transitionsthat are used when operating the system, and that are different from theplurality of state transitions; an operation registration unit thatreceives the definitions of the state transitions used when operatingthe system and registers the definitions in the additional statetransition storage unit; an availability analyzing unit that analyzesthe availability of the system based on the definitions of the statetransitions stored in the state transition storage unit and thedefinitions of the state transitions stored in the additional statetransition storage unit; an operation analysis unit that analyzes commonstate transition patterns in at least part of the definitions of theplurality of state transitions used when operating the system, andstored in the additional state transition storage unit; and an operationanalysis result output unit that outputs analysis results obtained bythe operation analysis unit.

(Additional Note 2)

The availability evaluation device according to Additional Note 1,wherein the operation analysis unit analyzes the common state transitionpatterns every time a predetermined number of definitions of the statetransitions used when operating the system are registered in theadditional state transition storage unit.

(Additional Note 3)

The availability evaluation device according to Additional Note 1,wherein the operation analysis unit analyzes the common state transitionpatterns every predetermined period.

(Additional Note 4)

The availability evaluation device according to any one of AdditionalNotes 1 to 3, wherein the operation analysis unit extracts a mostfrequent state transition pattern among the common state transitionpatterns, and the operation analysis result output unit outputsinformation indicating the most frequent state transition pattern.

(Additional Note 5)

The availability evaluation device according to Additional Note 4,wherein the operation analysis unit extracts a most frequent statetransition pattern for a predetermined transition source state among thecommon state transition patterns.

(Additional Note 6)

The availability evaluation device according to Additional Note 4,wherein the definition of the state transition used when operating thesystem includes information that indicates a transition probability ofeach state transition, and the operation analysis unit extracts a statetransition pattern having the transition probability of a predeterminedvalue or more, among the common state transition patterns.

(Additional Note 7)

An availability evaluation method comprising: storing in a statetransition storage unit definitions of a plurality of state transitionscorresponding to configurations of a system; storing in an additionalstate transition storage unit definitions of state transitions used whenoperating the system, which are different from the plurality of statetransitions; receiving the definition of the state transitions used whenoperating the system and registering the definitions in the additionalstate transition storage unit; analyzing the availability of the systembased on the definitions of the state transitions stored in the statetransition storage unit and the definitions of the state transitionsstored in the additional state transition storage unit; analyzing commonstate transition patterns in at least part of definitions of theplurality of state transitions used when operating the system, andstored in the additional state transition storage unit; and outputtinganalysis results on common state transition patterns.

(Additional Note 8)

A program for causing a computer including a state transition storageunit that stores definitions of a plurality of state transitionscorresponding to configurations of a system, and an additional statetransition storage unit that stores definitions of state transitionsthat are used when operating the system, and that are different from theplurality of state transitions, to implement: a function of receivingthe definitions of the state transitions used when operating the systemand registering the definitions in the additional state transitionstorage unit; a function of analyzing the availability of the systembased on the definitions of the state transitions stored in the statetransition storage unit and the definitions of the state transitionsstored in the additional state transition storage unit; a function ofanalyzing common state transition patterns in at least part of thedefinitions of the plurality of state transitions used when operatingthe system, and stored in the additional state transition storage unit;and a function of outputting analysis results on the common statetransition patterns.

10: AVAILABILITY EVALUATION DEVICE

20: VIRTUAL MACHINE SERVER

30: LIBRARY MANAGEMENT UNIT

32: STATE TRANSITION MANAGEMENT TABLE

34: OPERATION REGISTRATION UNIT

36: OPERATION REGISTRATION TABLE

38: ADDITIONAL STATE TRANSITION REGISTRATION TABLE

40: AVAILABILITY ANALYZING UNIT

42: AVAILABILITY ANALYSIS RESULT PRESENTATION UNIT

44: OPERATION ANALYSIS UNIT

46: OPERATION ANALYSIS RESULT PRESENTATION UNIT

I Claim:
 1. An availability analysis device having a processor andmemory, comprising: a state transition storage unit realized by thememory and configured to store definitions of a plurality of statetransitions corresponding to configurations of a system, each of thedefinitions of the plurality of state transitions including a transitionsource state, a transition destination state and a transitionprobability; an additional state transition storage unit realized by thememory and configured to store definitions of a plurality of additionalstate transitions that are used when operating the system and that aredifferent from the plurality of state transitions, each of thedefinitions of the plurality of additional state transitions including atransition source state, a transition destination state and a transitionprobability; an operation registration unit realized by the processorexecuting a program stored in the memory and configured to receive thedefinitions of the additional state transitions and register thedefinitions in the additional state transition storage unit; anavailability analyzing unit realized by the processor executing theprogram stored in the memory and configured to analyze an availabilityindicating a ratio of time where the system is in operation, based onthe definitions of the state transitions stored in the state transitionstorage unit and the definitions of the additional state transitionsstored in the additional state transition storage unit; an operationanalysis unit realized by the processor executing the program stored inthe memory and configured to analyze a number of occurrences of eachpair of the transition source state and the transition destination statein the definitions of the plurality of additional state transitionsstored in the additional state transition storage unit; and an operationanalysis result output unit realized by the processor executing theprogram stored in the memory and configured to output analysis resultsobtained by the operation analysis unit.
 2. The availability analysisdevice according to claim 1, wherein the operation analysis unit isconfigured to analyze the number of occurrences every time apredetermined number of definitions of the additional state transitionsare registered in the additional state transition storage unit.
 3. Theavailability analysis device according to claim 2, wherein the operationanalysis unit is configured to extract the pair having the largestnumber of occurrences, and the operation analysis result output unit isconfigured to output information indicating the pair having the largestnumber of occurrences.
 4. The availability analysis device according toclaim 1, wherein the operation analysis unit is configured to analyzethe number of occurrences every predetermined time period.
 5. Theavailability analysis device according to claim 4, wherein the operationanalysis unit is configured to extract the pair having the largestnumber of occurrences, and the operation analysis result output unit isconfigured to output information indicating the pair having the largestnumber of occurrences.
 6. The availability analysis device according toclaim 1, wherein the operation analysis unit is configured to extractthe pair having the largest number of occurrences, and the operationanalysis result output unit is configured to output informationindicating the pair having the largest number of occurrences.
 7. Theavailability analysis device according to claim 6, wherein the operationanalysis unit is configured to extract the pair having the largestnumber of occurrences for a predetermined transition source state. 8.The availability analysis device according to claim 6, wherein theoperation analysis unit is configured to extract the pair having thelargest number of occurrences in the additional state transitions eachhaving the transition probability of a predetermined value among theplurality of additional state transitions.
 9. An availability analysismethod comprising: storing in a state transition storage unitdefinitions of a plurality of state transitions corresponding toconfigurations of a system, each of the definitions of the plurality ofstate transitions including a transition source state, a transitiondestination state and a transition probability; storing in an additionalstate transition storage unit definitions of a plurality of additionalstate transitions used when operating the system, which are differentfrom the plurality of state transitions, each of the definitions of theplurality of additional state transitions including a transition sourcestate, a transition destination state and a transition probability;receiving the definition of the additional state transitions andregistering the definitions in the additional state transition storageunit; analyzing an availability indicating a ratio of time where thesystem is in operation, based on the definitions of the statetransitions stored in the state transition storage unit and thedefinitions of the additional state transitions stored in the additionalstate transition storage unit; analyzing a number of occurrences of eachpair of the transition source state and the transition destination statein the definitions of the plurality of additional state transitionsstored in the additional state transition storage unit; and outputtinganalysis results on the common state transition patterns.
 10. Anon-transitory computer readable medium storing a program for causing acomputer including a state transition storage unit configured to storedefinitions of a plurality of state transitions corresponding toconfigurations of a system, each of the definitions of the plurality ofstate transitions including a transition source state, a transitiondestination state and a transition probability, and an additional statetransition storage unit configured to store definitions of a pluralityof additional state transitions that are used when operating the systemand that are different from the plurality of state transitions, each ofthe definitions of the plurality of additional state transitionsincluding a transition source state, a transition destination state anda transition probability, to implement: a function of receiving theadditional definitions of the state transitions and registering thedefinitions in the additional state transition storage unit; a functionof analyzing an availability indicating a ratio of time where the systemis in operation, based on the definitions of the state transitionsstored in the state transition storage unit and the definitions of theadditional state transitions stored in the additional state transitionstorage unit; a function of analyzing a number of occurrences of eachpair of the transition source state and the transition destination statein the definitions of the plurality of additional state transitionsstored in the additional state transition storage unit; and a functionof outputting analysis results on the common state transition patterns.